Breast milk, the optimal source of nutrition for infants worldwide, contributes significantly to pediatric HIV-1, accounting for 44% of overall mother-to-child HIV-1 transmission events among antiretroviral-naive women. However, the majority of HIV-1 infected pregnant women in sub-Saharan Africa opt to breastfeed their infants because they are unable to practice replacement feeding. While exclusive breastfeeding has been associated with lower HIV-1 transmission risk and increased protection against infant morbidity and mortality, only a small proportion of HIV-1 infected women breastfeed exclusively during the first 4-6 months after delivery. Improving rates of exclusive breastfeeding may therefore have an important public health impact. Studies in which women have received supportive counseling as a strategy for increasing exclusive breastfeeding rates have demonstrated that HIV-1 uninfected women can adopt safer breastfeeding practices. We propose a stepped wedge cluster randomization intervention trial to be conducted within 6 government community clinics (clusters) in Nairobi to investigate the impact of improved counseling on breastfeeding practices among HIV-1 infected women. This design is particularly useful for evaluating population level impact of an intervention that has been shown to be effective at the individual level and it minimizes contamination between study arms. We will investigate whether providing additional counseling to HIV-1 infected women in clinic at 36 weeks gestation, and at 1 and 6 weeks postpartum (intervention arm) will result in increased rates of exclusive breastfeeding and fewer infant HIV-1 infections compared to rates in women who receive standard counseling provided by the prevention of mother-to-child transmission (PMTCT) program (control arm). The intervention phase will be preceded by a formative research study to understand better the reasons for low uptake of exclusive breastfeeding and to improve strategies for increasing exclusive breastfeeding. Focus group discussions will be conducted with women who have infants aged 0-6 months and have breastfed. Promotion and support of exclusive breastfeeding as an HIV-1 prevention strategy is an attractive and achievable option, especially in resource-limited settings. We anticipate demonstrating that this cost-effective intervention will result in increased exclusive breastfeeding rates, lower incident breast pathology, and fewer infant HIV-1 infections.